1. Field of the Invention
This invention relates to methods and apparatus for the photothermal treatment of tissue and, more particularly, to methods and apparatus for treating cutaneous and subcutaneous conditions at depth.
2. Description of the Related Art
The benefits of being able to raise and/or lower the temperature in a selected region of tissue for various therapeutic and cosmetic purposes has been known for some time. For instance, heated pads or plates or various forms of electromagnetic radiation, including visible, infrared and microwave radiation, electricity, and ultrasound have previously been used for heating subdermal muscles, ligaments, bones and the like to, for example, increase blood flow, to otherwise promote the healing of various injuries and other damage, and for various therapeutic purposes, such as frostbite or hyperthermia treatment, treatment of poor blood circulation, physical therapy, stimulation of collagen, cellulite treatment, adrenergic stimulation, wound healing, psoriasis treatment, body reshaping, non-invasive wrinkle removal, etc. The heating of tissues has also been utilized as a potential treatment for removing cancers or other undesired growths, infections and the like. Heating may be applied over a small localized area, over a larger area, for example to the hands or feet, or over larger regions of tissue, including the entire body.
Since most of the techniques described above involve applying energy to tissue at depth through the patient's skin surface, peak temperature generally occurs at or near the patient's skin surface and decrease, sometimes significantly, with depth. Further, while microwaves or ultrasonic and other acoustic radiation have been used in the past, such radiation has had limited use because, particularly for microwaves, they may be potentially mutagenic, may potentially otherwise result in cell or systemic damage and, particularly for acoustic sources, are relatively expensive. They may also not be practical for large-area treatment.
While optical and near infrared (NIR) radiation (collectively referred to hereinafter as “optical radiation” is generally both less expensive and, being non-mutagenic, safer than microwaves radiation, the use of optical radiation has heretofore not been considered suitable for most applications involving heating of tissue at depth, the term “tissue at depth” as used herein meaning tissue at the border zone of the dermis and hypodermis or subcutaneous region, some of which tissue may be in the lower dermis, mostly at a depth deeper than 1 mm, and tissue below this border zone to a depth of up to about 50 mm The reason why this radiation has not been considered suitable is because such radiation is both highly scattered and highly absorbed in surface layers of tissue, precluding significant portions of such radiation from reaching the tissue regions at depth to cause heating thereof. In view of the energy losses due to scattering and absorption, substantial optical (including NIR) energy must be applied in order for enough such energy to reach a region of tissues at depth to have a desired effect. However, such high energy can cause damage to the surface layers of tissue and pain/discomfort to the patient, making it difficult to achieve desired photothermal treatments in tissue regions at depth. For these reasons, optical radiation has heretofore had at most limited value for therapeutic and cosmetic treatments on tissue at depth.
While heating or cooling of tissue at depth alone has proved useful for many treatments, the combination of heating and cooling applied intermittently to the skin surface (known as contrast therapy) is also known and has been suggested for skin improvement, pain relief, inflammation reduction, and healing of injury. Of particular importance is the application of these techniques for reducing subcutaneous fat deposits and treating cellulite (gynoid lipodystrophy). However, use of cooling or heating, either alone or in combination for treatment of conditions at depth, for example for skin improvement, cellulite improvement, fat reduction, and treatment of other conditions has been limited by the body's pain/discomfort tolerance and by the damage limits of treated organs and adjacent, especially cutaneous, tissue that need to be kept intact.
A need therefore exists for improved method and apparatus for photothermal treatment of tissue regions at depth, and in particular for treatment of deep dermis and subcutaneous regions of tissue, which treatments provide improved treatment results, while both reducing patient pain and discomfort and protecting adjacent and other non-treatment tissue from damage.